Instal a Tone Stack Calculator and play with the values. Low frequency content also depends on the interstage filtration. But it's easy to end up with blocking distortion if you allow too much lows to pass.
With the values you've posted there's an increase in low frequency response but there's also shift in mids. Mid dip goes from 650Hz to 1.2kHz.
You can try C1 330p, R1 22k C2, C3 33n.
With the values you've posted there's an increase in low frequency response but there's also shift in mids. Mid dip goes from 650Hz to 1.2kHz.
You can try C1 330p, R1 22k C2, C3 33n.
I would add switchable paralell cap to C1. Let's name it C1' - anything between 330p and 1n. Just test what suits you best.
Another mod - R1: replace 33k with 15k and add 20k or 25k potentiometer in series with R1.
Below you have simulation of the modded R1 range - from 15k (top) to 36k (bottom).
With the values you've posted there's an increase in low frequency response but there's also shift in mids. Mid dip goes from 650Hz to 1.2kHz.
You can try C1 330p, R1 22k C2, C3 33n.